Peter H. Bull

Compressive Failure of Impacted NCF Composite Sandwich Panels - Characterisation of the Failure Process

In the present study, non-crimp fabric (NCF) composite face sheet sandwich panels have been tested in compression after impact (CAI). Damage in the face sheets was characterised by fractography. Compression after impact loaded panels were found to fail by plastic fibre microbuckling (kinking) in the damaged face sheet. Studies of panels for which loading was interrupted prior to failure revealed extensive stable kink band formation at several positions and in numerous plies. Kink bands initiated and propagated within a wide region close to the point of impact. In addition, kink bands initiated in zones with high shear stresses, away from the impact centre line. Consequently, the fractographic results from this investigation do not support the assumption of modelling the impact damage as an equivalent hole. To achieve accurate predictions of kink band initiation, the stress field must be known. The results from this study imply that bending effects caused by remaining dent or material eccentricities in the damaged region must be considered.

High-Velocity and Quasi-Static Impact of Large Sandwich Panels

An investigation of the response of sandwich structures subjected to impact velocities of virtually 0 m/s and approximately 1000 m/s is conducted. The higher velocity exceeds both the longitudinal and the transverse wave propagation velocities of the core material in the sandwich panels. The objective is to investigate the possibility to simulate the damage from ballistic impact of sandwich panels through quasi-static experiments. Panels are impacted using a 40mm Bofors AA gun and, using a similar projectile, other panels are indented quasi-statically. Energy absorption is measured in both test series. After impact, the panels are tested in in-plane compression together with one undamaged panel for reference. Residual strength of impacted panels is analyzed by finite element analysis. It is shown that the damage from high-velocity impact is limited, and it is possible to regain most of the undamaged strength by repair.

Empirical Study of Flight-Dynamic Influences on Radar Cross-Section Models

In this work, measurements and a method for analyzing flight-dynamic effects on radar cross-section models for aircraft are presented. Flight-dynamic effects need to be considered when designing co ...

Curved Sandwich Beams with Face–Core Debond Subjected to Bending Moment

Curved sandwich beams subjected to opening bending moment are studied. Face–core debonds of varying size are introduced at the compressively loaded face sheet and the structural integrity is investigated. Analytical and finite element models are compared in order to identify the governing failure modes of the beams. A simple expression is presented as a tool for getting a quick estimate of the severity of an interface crack in a curved sandwich beam. Five different configurations of beams are tested experimentally in a custom made bending rig.

Ballistic impact facility - considerations and experiences

A facility for testing of ballistic impact has been designed and developed. The goal was to develop a facility which was relatively easy to use and modify, as the requirements for the testing equipment changed with different research projects, e.g. students projects [1]. The setup consisted of a compressed air gun with an exchangeable barrel, a speed trap for measuring the incident velocity and a kinetic pendulum which both served as a means to measure the residual energy of the projectile and to catch the projectile from further travel. The aim of this paper was to cover some of the experiences encountered during the design and development high velocity impact test equipment.

Concurrent Bending and Localized Impact on Sandwich Panels

The paper describes impact/bending testing of sandwich panels with 10 mm foam core and FRP face-sheets, with emphasis on test procedures, registration of results and description of the specialized test equipment developed. The sandwich panels were subjected to a cylindrical bending load of varying magnitude, while impacted at approximately 500 m/s. The impactor body was a steel sphere, diameter 10mm, with a mass of approximately 4g. The energy absorption and damage morphology of preloaded panels were compared with similar data for impact on specimens without preload. A high-speed camera was used for qualitative registration of panel response.